Carrier transmission system



l 1927. Feb 'M. B. LONG CARRIER TRANSMISSION SYSTEM Fild March 31, 1925 4 Sheets-Sheet 1 vRFQ //7 van/0r: MGM/7C6 5 Long Feb. 1 1927.

Recflfiad Current in milliamperes. E, 2 I I 1,615,988 M. B. LONG CARRIER TRANSMI S S I 0N SYSTEM Filed March 31; 1925 4 Sheets-Sheet 2 .04 .oo .08 .m .|2 .|4 .m

'Curreni input to amplifierin milliamperes mvenfor: Maurice B. Lang Feb; 1 ,1927. v 1,615,988

M. B. LONG CARRIER TRANSMISSION SYSTEM Filed March 31, 1925 4 Sheets-Sheet 5 inn/anion I Maurice 53 Long.

Feb. 1 1927. 1,615,988

M. B. LONG CARRIER TRANSMISSION SYSTEM Fild March 31, 1925 4 Sheets-Sheet m2, @z m ZPF 190/72 19/?1 Y 2425 22 I 25 g 12F fip/z gg 50% Wye/War."

Maurice 53 Long by Af/j/ Patented Feb. 1,192.7.

' UNITED sIeTEs' 1,615,988 PATENT OFFICE.

MAURICE 3. LONG, 01 EAST ORANGE, NEW JERSEY, ASSIGNOR T WESTERN ELEC- TBIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

emma TRANSMISSION sis'rnu.

Application filed larch a1, 1923. Serial no. eeaoo'r.

. This invention relates to a carrier transp mission system, and more particularly to a multiplex carrier telegraph system employing carrier currents of audio fre uency.

Such a multiplex carrier telegrap systemv employing carrier currents of audio frequency may be utilized to advantage on long such a long distance telephone line without changing in any wise the usual. line equipment such as loading coils, amplifying repeaters, filters and other apparatus.

Such a multiplex audio frequency carrier 7 telegraph system may be applied in similar Ill) manner to a channel of an existin multiplex high frequency carrier or a multiplex radio telephone system.

Among the objects of the invention are: To provide an eficient and economical multinlex-carrier telegraph system operating with carrier currents of audio frequency.

To provide a multiplex carrier systemwherein modulatio between channels of different systems operating with carrier cur rents of the same frequency from the same source and between adjacent channels of c the same system operating with carrier curi system employing carrier currents of audio frequency which may be applied efliciently rents of different frequencies is so reduced as to be negligible.

To improve the quality of the transmitted marking and spacing signals.

To provide a carrier telegraph system wherein the marking signals are unbiased.

To provide in a receiving channel of a carrier current system a' receiver which discriminatesbetween signal currents and interfering line currents of smaller am litude.

To provide a multi lex carrier te egraph and economically to a channel of a multiplex radio or a multiplex high frequency carrier telephone system.

In the drawings,

Fig. 1 shows diagrammatically the terminal apparatus and circuits of a multiplex audio frequency carrier telegraph system.

Fig. ,2 shows a modulating circuitso organized as to improv the quality of the transmitted signals.

Fig. 3 shows a curve illustrating the voltampere characteristic of the carrier" frequency generator.

Fig. 4 shows input output curves for the detector rectifier. 1 I

Fi 5 shows the form of signals produce by the modulating circuit of Fig. 1 and the corresponding received signals.

Fig. Sshows the form of signals produced by the modulating circuit of Fig. 2 and. the 65 corresponding received signals.

Fig. 7 shows diagrammatically transmitting and receiving channels of a multiplex high frequency carrier telephone system to which the multiplex audio frequency tele- 7o graph system of Fig. 1 may be applied.

Fig. 8 shows diagrammatically a; multiplex radio telephone system to which the multiplex audio frequency carrier telegraph system of Fig. 1 may be applied.

Fig. 1 showing a multiplex carrier telegraph system employing carrier waves of audio frequency will first be described.

This system comprises a main line EL over which modulated carrier waves are to be transmitted in one direction, a main line WL for transmission in the opposite direction, and a plurality of transmitting channels TL TL etc., and receiving channels BL R11 etc., to connect a plurality of ordinary Morse telegraph equipments to the main lines.

While only so much of the Morse tele graph e uipment as is necessary for an understanding of the invention is shown, it will he understood that Morse telegraph equipment such as shown in Fig. 55 of the article by Colpitts and Blackwell on Carrier current telephony and telegraphy in Transactions of American Institute of Electrical Engineers, vol. 40, 1921, may be associated with the transmitting and receiving channels. I

The transmitting channels TL TL and TL are coupled to the main line EL through a transmitting terminal amplifier-TTA commqn to all such channels at the same termina The receiving channels RL RL and RL, are coupled to the main line WL through a receiving terminal amplifier RTA common to all such channels at the same terminal.

While for purpose of illustration only two transmittingand two receiving channels are fully shown, it will be understood that more Gil may be and, in practice, usually are provided;

The outgoing channels.TL,, TL and TL are respectively supplied with carrier currents of different frequencies from th carrier frequency generators G Gr and G It will be understood, of course, that a separate generator or source of carrier current will be provided for each channel of the same system transmitting in the same direction. A multiple frequency rotating generator, such as disclosed in the copending application of Hugh M. Stoller Serial .No. 644,071, filed June 8, 1923, or a harmonic oscillation generator may be employed.

Since separate main lines are employed for transmission in opposite directions, carrier currents of like frequencies may be employed for transmission over each line.

The carrier frequency generators G Gr and G may be common to a plurality of rlii ultiplex carrier systems like that shown in Thus these generators, as illustrated, also supply carrier currents to the transmitting channels of other multiplex audio frequency carrier telegraph systems, .one of which is indicated by the transmitting channels 'IL' TL, and TL' In carrier transmission wherein a plurality of multiplex carrier signal systems are supplied with carrier currents from aplurality of, generators or sources common thereto two kinds of interchannel modulation originating at the transmitting terminal may occur as follows.

1. Modulation between channels of different systems operating with carrier currents of the same frequency.

2. Modulation between channels of the same system operating with carrier currents of different frequencies.

Means are provided to limit such interchannel modulation to such an amount that the amplitude variations of the signals resulting therefrom do not cause any interference with the reception of signals.

' The receiving channels are provided with means for increasing the current amplitude discrimination of the receiving relays, so that the proper operation of such relays is not affected by the superposed interfering line currents of smaller amplitude including among others those interfering line currents resulting from interchannel modulation.

All transmitting channels are similar, so a description of one will suifice.

The transmitting channel TL includes a modulating circuit or modulator M and a transmitting band filter TBF The modulating circuit M comprises two impedance elements 1 and 2 included serially therein, an impedance element 3 in bridged relation to the circuit, and a transmitting element or switch 4 having marking and spacing contacts M and S for controlling the marking and spacing signals to be transmitted.

' Impedance elements 1, 2 and 3 may take the form of non-inductive resistances.

The impedance of element 1 must be of such value that when the switch 4 is closed and opened to control the spacing and marking signals over its channel the impedance change in the modulating circuits of the channels in other systems to which carrier currents of the same frequency aresupplied from the same source, will not be sufficient to cause noticeable interfering modulation in such other channels.

More particularly, the adjusted value of the impedance of element 1 which limits the carrier current supplied to the input of the modulating circuit to a predetermined value, must be such that the summation of all carrier currents supplied from the same source to simultaneously operating channels does not exceed a value determined by the generator volt-ampere characteristic as will more fully hereinafter appear.

During a spacing signal, the element 3 is short circuited and the load on the generator is represented by the current through impedance 1. Impedance element 1 therefore serves to protectthe generator against short circuit.

During a marking signal, the short circuit is removed from element 3, and the load on the generator is represented by the current through impedance element 1 in series with element 3 shunted by element 2 in series with the surge impedance of band filter TBF The generator voltage therefore varies while signals are being transmitted, the magnitude of such variations depending upon the number of simultaneously operating channels and the relative values of impedance elements 1, 2 and 3 and the surge impedance of the band filter.

If the variation in voltage is large when changing from marking to spacing signals or vice versa, the modulation between chan nels operating with carrier currents of the same frequency maybe so great as to cause interference'wlth the reception of the. signals. This interference takes the form of crossfire or crosstalk which increases or de creases the amplitude of the signals and tends to break them up.

It is therefore important that this modulation between channels operating with the same carrier frequency be limited to such an amount as will not cause interference with the reception of signals.

Such modulation is the most when the marking 'contacts of all the channels operat-' same carrier frequency is not sufficient to cause interference with the reception of signals.

The impedance of element 1 therefore I bears such a relation to the impedance of elements 2 and 3 and the surge impedance of the band filter TBF as Viewed from the modulating circuit, that there is not more than a ten percent variation in generator voltage when changing from marking to spacing si nals or vice versa.

Fig. 3 slhows the volt-ampere characteristic of the generator with current output plotted as abscissae against terminal voltage as ordinates.

'Whenall channels, supplied with current of the same frequency, are simultaneously transmitting spacing signals the current drawn from the generator is represented by L and the terminal voltage by V When all such channels are transmitting marking signals the current drawn from the generator is represented by Im and the terminal voltage by V,,,. V, represents the open circuit terminal voltage of the generator.

Thus during the transmission of marking and spacing signals by't-he channels operating with the same carrier frequency, the terminal voltage of the generator cannot vary more than V V Consequently the modulation between such channels is not suflicient to cause interference with the reception of signals.

The combined impedance of elements 2 and 3 approximates the surge impedance of thetransmitting band filter TBF as viewed from the modulating circuit M The value of the impedance of element 2 is dependent upon the frequency spacing of the channels of the multiplex carrier system.

The impedance of element 2 must be such that, when the switch 4 is being operated to control the marking and spacing signals, the resulting change in impedance of the transmitting band filters of adjacent channels is not suficient to interfere with the proper operation of such other channels.

The frequency spacing of the channels may be great enough so that the value of the impedance of the element 2 may be reduced to zero, in which case the impedance of element 3 would approximate the surge impedance. 7

Ordinarily as the frequency spacing of the channels becomes closer, the Value of.

the impedance of element 2 should increase. The shunting'efiect of the band filter of each transmitting channel upon the band filters of the adjacent transmitting channels on each side thereof with a. given 'freuency spacing of channels and design of 'ters is determined bythe impedance termination for the input of the filters. 1 When the impedance termination changes while signals are being transmitted, the energy absorbed from adjacent operating channels by the filter of an operating transmitting channel varies. This variation in energy absorption produces modulation between adjacent channels of the same system operating with carrier currents of different frequencies, thereby causing the amplitude ofthe signals to vary;

This signalamplitude Variation, if of any considerable magnitude interferes with the reception :of signals causing them to be broken up.

It is important therefore that the variations inener y absorbed by each filter from the filters 0 adjacent channels be limited to such magnitude as will not interfere with the proper reception of the signals.

As previously stated the frequency spacing of the channels of the same system may be great enough so that impedance 2 may be reduced to zero, in which case the filter termination varies from zero to an impedance approximating the surge impedance of the filter while signals are being transmitted.

As the frequency spacing becomes closer, the change in impedance termination of the filters during the transmission of signals should become less. This may be accomplished by increasing the ratio of impedance 2 to impedance 3.

The switch 4 provided with a marking contact M and a spacing contact S is controlled by the sending relay 6 of the ordinary Morse telegraph equipment.

The sending relay 6 is controlled. by a sending key 7.

When the sending key? is not being op erated a switch 8 is closed to hold the relay 6 energized and thereby hold the spacing contact S open. When the sending key 7 is to be operated the switch 8 is opened by moving it to its dotted line position.

The transmitting band filter TBF may be of the general type disclosed in U. S. patents to George A. Campbell 1 Nos. 1,227,113 and 1,227,114 dated May 22, 1917. It is designed to pass only currents of the carrier frequency assigned to the transmitting channel TL and currents of the frequencies within the upper and lower side ceiving band llter RBF an amplifier A and a rectifier R The receiving band filter RBF is similar to the transmitting band filter TBF It is designed to pass only carrier currents of the frequency assigned to the receiving channel RL, and currents of frequencies within the upper and lower side bands of such. carrier frequency and to suppress currents of all other frequencies.

The amplifier A inductively coupled to the receiving band filter RBI! may be of any Well known type but as illustrated is a three element relay of the space current type The rectifier R may be of any well known type, but as illustrated is asimilar space current type relay.

The input current to the amplifier A is rgeulated by a potentiometer 9.

The output circuit of the amplifier A .is

inductively coupled to the input circuit of the rectifier R, through a transformer 10.

The rectifier R, controls the receiving relay 11 of the ordinary Morse telegraph equipment (not shown).

The relay 11 has three windings, one of which is included directly in the output circuit of rectifier B A second winding is inductively coupled with the rectifier output circuit through the transformer 12. This second winding commonly called the kick winding insures the quick response of the relay toreceived signaling currents. The third winding in series with a battery or other source of current is a biasing winding which biases the relay armature to one position.

'When a certain value (for example 5 milliamperes) of signal current; is delivered to the input circuit of the rectifier R the receiving relay ll responds to a predetermined rectified current in the rectifier output circuit.

To prevent false operation of the receiving relay due to interfering line currents superposed upon the signal currents means are provided whereby amplitude discrimination is obtained and the relay is unafi'ected and is not responsive to such superposed interfering line currents.

The means for obtaining such amplitude discrimination comprises an impedance 13 which may take the form of a high resistance, included serially in the input or grid circuit of the rectifier R To obtain a high degree of amplitude discrimination as indicated by the curves of Fig. 4 it has been found that the impedance 13 should be connected in the grid circuit between the battery 14 and the secondary winding of the input transformer 10.

In Fig.- 4 input current from the line impressed upon the amplifier A, is plotted as abscissee against rectified current from the rectifier It, as ordinates.

Curve A. shows that when impedance 13 is not included in the grid circuit, small variations of input current cause correspondingly great changes in rectified current.

Therefore when the impedance 13 is not employed the superposed interfering line currents are reflected into the output circuit oft-he rectifier R, and cause the false operation of the receiving relay l1.

Curve B shows the rectified current variations for variations in input current when impedance 13 is connected between the secondary winding of the output transformer and the grid of the rectifier R According to this curve B for small changes in input current corresponding changes in the rectified current. are comparatively great at or near the value of the rectified current (5 milliamperes) at which the receiving relay 11 operates, so the relay is affected by the superposed interfering line currents. Furthermore the efliciency of the receiving circuit is greatly decreased, for much greater input is re uired to obtain the proper value of rectifie current for operating the receiving relay.

Curve C represents the variations in rectified current for amplifier input variations when impedance 13 is connected as shown in Fig. 1.

This curve shows clearly that at and near 5 milliamperes rectified current atwhich the receiving relay 11 operates changes in input current cause but relatively small changes in rectified currents. These small changes in rectified current do not affect the operation of the receiving relay.

The operation of the system of Fig. 1 is as follows assuming that signals originating in the Morse telegraph equipment associated with transmitting channel TL are to be transmitted.

The operator after opening the switch 8 closes and opens the telegraph key 7 to form and transmitmarking and spacing signals.

The closure of key 7 to initiate a marking signal causes the sending relay 6 to operate, thereby moving the transmitting element 4 from the spacing to the marking contact.

Opening of the spacing contact removes the short circuit from impedance element 3, thereby allowing currents of the frequency assigned to channel TL to pass through band filter TBF, into the transmitting terminal amplifier TTA. The amplified cur rent from the terminal amplifier is impressed upon the main line EL.

increase The duration of closure of key 7 determines whether the marking signalis a dot or a dash.

The opening of key 7 causes the sending relay 6 to release the transmitting element 4 which thereupon moves from its marking to its spacing contact.

When the transmitting element 41. engages the spacing contact S, impedance element 3 is short circuited thereby removing current of the frequency assi ned to channel TL from the band filter T F and consequently from the line EL.

A spacing signal is represented by the length of time between marking signals when current is removed from the line.

It will be observed that during a marking signal current is passing to line for a greater length of time than the duration of closure of the sending key 7 This difierence is measured by the time of travel of the transmitting element 4 from the marking to the spacing contact. Therefore the marking signals are biased as will more fully appear.

The signals transmitted over the main line EL are received by the particular receiving channel at the distant terminal to which are assigned carrier currents of the frequency assigned to the transmitting chan nel TL v Inasmuch as the apparatus and circuits for only one terminal are shown, the operation of the system with respect to the reception of signals incoming over the main line WVL will be described. a

The marking signal currents incomin over the main line WL are impressed upon the receiving terminal amplifier ETA and the amplified currents-therefrom are selected by the band filter in the proper receiving channel.

Assuming that the carrier currents of the operating'transmitting channel at the distant station are of the frequency assigned to the receiving channel BL the incoming amplified signal currents from the receiving terminal amplifier are selected by the band filter RBF The marking signal currents from the band filter lit-BF pass through the potentiometer 9 and then after being amplified by the amplifier A are impressed u on the input of the rectifier R The recti ed currents cause the receiving relay 11 to 0 state and close its working contact 15 whic 1 controls the sounder or other receiving'device in the Morse telegraph equipment associated with the receiving relay-11 of the receiving channel RL Upon the cessation of the marking signal receiving relay 11 releases opening its working contact 15. I

According to one wa in which the invention may be practice a multiplex audio frequency carrier telegraph system having circuits are given-the values sett'orth below and impedances 13 in the receivin circuits are given a value of two megohms t 1e modulation between channels of diderent systems operating with carrier currents of the same frequency and between channels of the same system operating with carrier currents of difierent frequencies is not sufficient to cause interference with the proper reception of signals.

Element. Impedance.

1 2000 ohms. 2 350 ohms. 3 V 700 ohms.

heavy bias meaning that the received signal' is of greater duration than the closure of the sending key.

Whether or not the signals are biased is not of so great importance when the system is being operated at low speed. However, when operating at high speed it is important that the signals be without bias as'biased signals may interfere seriously with the proper reception thereof. As the speed of operation increases, the bias becomes relatively greater for the time of travel of the trans mitting element 4 from the marking to the spacing contact does not change.

The formation and transmission of a marking signal by the modulating circuit of Fig. 1 actually begins when switch 4 disengages the spacing contact S and continues until this contact is again engaged by the switch. v I

lit will be evident therefore, that, due to the time of travel of the switch 4t between the spacing and marking contacts, the duration of the transmitted and received marking signals is actuall greater than the duration of closure of t e sending key. This difi'erence is measured by the time of travel of the switch 4 from the marking contact M to the spacing contact S.

As to the modulating circuit of Fig. 2, it

will be seen that while a marking signal is being formed and transmitted current 1s on the line from the time switch 4 disengages the spacing contact S until this contact is again engaged by the switch. However, while the switch 4 is traveling from the spacing to the marking contact and is returning from the marking to the spacing contact current or a predetermined amplitude passes to line. When the switch is in engagement with the marking contact current of greater amplitude passes to line. These difi'erent line current conditions are brought about the peculiar organization of apparatus 1n the modulating circuit. Thus, while the switch 43 is moving from the s acing contact 5 to the marking contact iv and likewise during its return movement the short circuits are removed from both impedance elements 2 and 3 so current of a predetermined amplitude passes to line. While the switch 4;- is in engagement with the marking contact ll i impedance element 2 is short circulted so that current of greater amplitude passes to line.

When the modulating circuit of Fig. 2 is employed, the receiving relay 11 operates in response to the opening of the spac ng contact and releases in response to opening of the marking contact.

Consequentl as will be more fully here nafter pointed out, the received marking signal is without bias and corresponds in duration to the length of time the sending key is closed. 7

When the impedance elements of the modulating circuit of Fig. 2 are given the values set forth below, the inter-channel modulation originating at the transmitting terminal is not sufiicient to cause interference with the proper reception of signals.

Element. Impedance.

1 2000 ohms. 2 700 ohms. 3 700 ohms.

It will be observed that due to the factthat elements 2 and 3 are of the same impedance the band filter has the same imp edance termination while the transmitting element 4- is in engagement with either contact. While the element 4 is traveling be."

tween the contacts, the impedance termina Figs. 1 and 2 may be better understood, reference is made to Figs. 5 and 6 showing curves which illustrate the signals from the time they are initiated by the sending key until they are received at the sounder or signaling device at the distant terminal. 7

Fig. 5 shows a series of curves illustrating the condition of the signals transmitted by the modulating circuit of Fig. l.

The marking signals represented are dots (short curves) and dashes (long curves), the spaces therebetween representing the spacing signals.

he curves are in vertical alinement so as toafiord ready comparisons.

The curves A indicate the duration of closure of the sending key 7 for the marking signals.

Curves 13 indicate the magnitude and duration of the direct current applied to the sending relay 6.

Curves C indicate the magnitude and 'duration of the carrier current passing to line during the time that the transmitting element or switch 1- is off its spacing contact.

It will be noted that carrier current is passing to line for a greater length of time than the sending key 7 is closed, the differones being represented by the time of travel of the switch 4 from the marking to the spacing contact.

Curves D indicate the magnitude and duration of the rectified current flowing through the operating winding of the re ceiving relay 11.

The duration of this current flow exceeds the duration of closure of the sending key 7.

Curves E represent the corresponding current flow-in the kick winding of the receiving relay 11.

Curves F represent the combined current flow (curves 1) and E) through the operatlng and kick windings which is effective for operating the receiving relay.

The receiving relay operates when the magnitude of operating current is slightly greater than that represented by the dotted line f-f and releases'wlien the magnitude of the operating current is slightly less than that represented by the same dotted line.

be receiving relay therefore remains in operated condition for a greater length of time than the length of time that the sending key 7 is closed.

Curves G represent the magnitude and duration of the signal current in the sounder of other signaling device controlled by the -recei ving relay armature and its contact 15.

Curves H 1'epre:entthe duration of the received signals at the sounder or other signaling device Snot shown) controlled by the receiving re ay 11.

Inspection of these curves shows that the transmitted and received marking signals condition of the Jun (ill

have a heavy bias and that the spacing signals have a light bias.

The biasing of the signals does not interfere with the proper reception of the signals in a system operated at low speed,

but may become troublesome and cause interference with the proper reception of the signals if the system is operated at high s eed.

Fig. 6 shows corresponding curves illustrating the condition of the -s'gnals when the modulating circuit of Fig. 2 is employed. These curves 'nre designated by. the same set of reference characters as employed in Fig. 5 so that comparisons may readily be made.

Referring to curve F of Fig. 6, the receiving relay operates when the magnitude of the operating current is slightly in excess of that represented by the dotted line f-f and releases when it is slightly lacs than that represented by the dotted line.

Inspection of these curves of Fig. Sshows clearly that the received signals correspond in duration to the length of closure of the gending key 'Z- and are therefore without me. If a receiving relay without a kick winding is used, curves E and h do not apply, and the relay will operate when the rectilied current increases to a magnitude represented by the dotted line oZ-d and releases when the rectified current decreases to a magnitude represented by the dotted line rZ--d.

llnspection of curves D shows that the marking signal (Fig. 5) transmitted by the modulating circuit of Fig. l is biased while that (Fig. 6) transmitted by the modulating circuit of Fig. 2 although shifted along a time axis is unbiased.

Fig. 7 shows the terminal arrangement of a multiplex high frequency carrier system, to channels of which the multiplex audio frequency carrier telegraph systems like those shown in Fig. 1 may be connected.

The terminal arrangement comprises a plurality of transmitting channels T1L9 T L, T L and T 1 and a plurality of corresponding receiving channels E la, R 11, R 11 and R, L connected to'a high frequency line ML.

This high frequency carrier system operates upon the group frequency basis, the carrier currents for transmission in one direction being of frequencies within one group and those for transmission in the opposite directionbeing of frequencles Within another group. All frequencies of one group are higher than those of the other group.

High pass and low pass directional filters HGF and LGF are provided for the purpose of separating currents of frequencies within one group from those of frequencies w1thi n the other group.

These filters may be of the general typedisclosed in the Campbell patents, supra.

filters being provided, as shown, to separate the lower audio and higher carrier frequency currents.

The multiplex audio frequency carrier telegraph system of Fig. 1 may be'applied to a sendmg and a receiving channel of the .high frequency carrier system (Fig. 7) by connectin the secondary winding of the transmitting output transformer 16 and the primary winding of the receiving input transformer 1? (Fig. 1) to the respective terminals 18 and 19 (Fig. 7) of the trans filglng and receiving channels T L and Since all of the high frequency transmitting and receiving channels are similar, only a portion thereof have been illustrated.

The high frequency channel T L includes a modulator M-l and a transmitting band filter T Blt The modulator ltd-1 may be of any well known type, such, for example, as the vacuum tube modulator disclosed in Fig. 9

of the. Golpitts and Blackwell article, supra.

A carrier source CS supplies high fregvuency carrier current to the modulator The transmitting band filter T lBF, of the general type disclosed in the Campbell patents, supra, is designed to pass currents of the carrier frequency assigned to its channel and currents of frequencies within either the upper or lower side band of the carrier and to suppress currents of all other frequencies.

The high frequency channel B L includes a receiving band filter R 31 a demodulator Dl/l-l and alow pass filter LPF The receiving band filter R BF is similar to the transmitting band filter T BF. It is designed to pass currents of the carrier frequency assigned to its channel and currents of frequencies within citherthe upper or lower side band of the carrier and to suppress currents of all other frequencies.

The demodulator DM1 may be of any well known type, such as, for example, the vacuum tube demodulator disclosed in Fig. 9 of the Colpitts and Blackwell article, supra,

Ill)

Thei low pass filter LPF which may be of the type disclosed in the Campbell patents, supra, is designed to pass currents of the frequencies in accordance with which the high frequency carrier currents asslgned to this channel are modulated and to suppress currents of higher frequencies.

The marking signals originating in the transmitting channel TL of the multiplex audio frequency carrier telegraph system and transmitted from the transmitting terminal amplifier TTA are impressed upon the modulator M1. The currents comprising the marking signals so impressed upon the modulator M1 modulate the high frequency carrier currents from the source CS. The modulated carrier currents are then transmitted to the band filter T BF which suppresses one of the side bands. The other side band and the carrier are transmitted through the high pass directional filter HGF to the high frequency line ML.

High frequency carrier currents modulated'in accordance with the currents comprising the marking signals incoming from the line ML pass through the low pass directional filter LGF and are selected by the receiving band filter R BF. The modulated high frequency carrier currents transmitted through the band filter R,BF are impressed upon the demodulator DM-1, where they react with the unmodulated high frequency carrier currents incoming from the line ML. Currents resulting from interaction of the received line currents are transmitted *to the low pass filter LPF which permits the passage of currents of the frequency in accordance with which the high frequency carrier currents were modulated but suppresses currents of higher frequencies. Such currents as pass through the low pass filter LPF are transmitted through the receiving terminal amplifier ETA and are selected by the receiving band filter RBF These selected currents transmitted from the band filter RB]? are impressed upon the amplifier A The amplified currents from amplifier A, are impressed upon the input circuit of the rectifier R The resulting rectified signal currents operate the receiving relay 11, which closes its contact 15 thereby causing the operation of the usual sounder or other signal receiver of the Morse telegraph equipment.

Referring further to Fig. 7 it will be noted that the high frequency transmitting and receiving channels T L and R L couple a low frequency speech transmission line L to the high frequency main line ML.

These channels T L and R,L are equipped with apparatus similar to that included in the channels T L and B L previously described.

The low frequency speech transmission line L is associated with the high freqiency transmitting and receiving channels T and R L by means of a hybrid coil 20.

The two channels T L and R L are rendered substantially conjugate by the provision of an artificial line or net AL to balance the line L.

While only one transmitting and receiving channel of the high frequency carrier system is illustrated as having applied thereto a multiplex audio frequency carrier telegraph system like that shown in Fig. 1, it will be understood that'one or more of the other hi h frequency channels may have such an auc 1o frequency carrier telegraph system applied thereto.

Thus if it is desired to apply an audio fre quency carrier telegraph system to the high frequency transmitting and receiving channels T L and R 14 this may be done by sub stituting such system for the apparatus shown to the left of the dotted line X-X of Fig. 7.

Fig. 8 shows the terminal arrangement of a multiplex radio telephone system, to the channels of which multiplex audio frequency carrier telegraph systems, such as shown in Fig. 1, may be connected.

The terminal arrangement comprises a plurality of transmitting channels TRL TBL TRL and TRL coupled to a transmitting antenna and a plurality of corresponding receiving channels RRL RRL RRL and REL, coupled to a receiving antenna.

The mutiplex audio frequency carrier telegraph system of Fig. 1 may be applied to a transmitting and a receiving channel of the multiplex radio telephone system of Fig. 8 by connecting the secondary winding of the transmitting output transformer 16 and the primary winding of the receiving input transformer 17 (Fig. 1) to the respective terminals 21 and 22 (*Fig. 8) of the transmitting and receiving channels TEL and HEL Since all of the radio transmitting and receiving channels are similar, only a portion thereof have been illustrated.

The radio transmitting channel TRL includes an amplifier RA a modulator RM and a transformer 23.

The amplifier RA, and the modulator RM may be of any well known type, such as, for example, the vacuum tube amplifier and modulator disclosed in Fig. 9 of the Colpitts and Blackwell article, supra.

A carrier source RG93 supplies high frequency radio currents to the modulator RlVL.

The circuits of the transformer 23 are tuned bymeans 0f the condensers 2d and 25 to the radio frequency assigned to the channel TRL The transformers of the other transmitting channels are similarly tuned to therespective carrier thereto.

Theradio receiving channel BBL, includes a transformer 26 for coupling to the receiving antenna, a demodulator RUM, and

frequencies assigned a low pass filter LPF.

lid

lit?

The transformer 26 is a loosely coupled step-up transformer and is tuned by means of condensers 2'? and 28 to the radio carrier frequency assigned to the receiving channel RRL The demodulator RDM may be of any well blown type, such as, for example, the vacuum tube demodulator disclosed in Fig. 9 of the Colpitts-Blackwell article, supra.

The low pass filterLlPF which may be of i the general type disclosed in the Campbell patent supra, is'designed to pass currents of the frequencies in accordance with which the radio frequency currents assigned to this channel are modulated, and to suppress currents of higher frequencies.

' The marking signal currents originating in the transmitting channel TL, of the multiplex audio frequency carrier telegraph system are transmitted from the transmitting terminal amplifier 'lTA and impressed upon the modulator'Rhl The currents so 1mpressed upon the modulator modulate the radio frequency currents "from the source RG8 lhe modulated and unmodulated components of the radio frequency currents pass through the tuned antenna coupling and are transmitted from the transmitting antenna.

Modulated and unmodulated components of radio frequency waves incoming at the receiving antenna are selected by the tuned coupling in the receiving channel REL, and are then impressed upon the demodulator RDM These currents interact in the dc modulator and the currents resulting from such interaction are transmitted to the low pass filter LPF which permits the passage of currents of the frequency in accordance with which I the radio frequency currents were modulated and suppresses currents of higher frequencies. Such currents as pass through the low pass filter LPF are transmitted through the receiving terminal am plifier lit-TA and are selected by the receiving band filter RBF lfhese selected currents transmitted from the band filter RBF are impressed upon amplifier A The amplified currents from the amplifier A, are

then impressed upon the input circuit of the rectifier R The resulting rectified signal currents operate the receiving relay ill,

which closes its contact 15, thereby causing the operation of the usual sounder or other signal receiver of the Morse telegraph equipment associated with the receivm relay.

eferring further to Fig. 8, it will be noted that the radio transmitting and receiving channels TRL and REL couple a low frequency s ech transmission line L to the transmitting and the 'receivin antennee. These channels TRL, and RR 2 are equipped with apparatus similar to that included in the channels TEL and BBL, previously described.

The low frequency speech transmission line L is associated with the radio transmitting and reccivin channels by means of a h brid coil 29, an the two channels'are ren cred substantially conjugate by the pro vision of an artificial line or net AL to balance the line L.

While only one transmitting and receiving channel oi the radio system is illustrated as having applied thereto a multiplex audio frequency carrier telegraph system like that shown in Fig.1, it will be understood that one or more of the other transmitting and receiving radio channels may have such an audio frequency carrier telegraph system applied thereto Thus, if it is desired to apply the audio frequency carrier telegraph sys= tem'to the radio transmitting and receiving channel 'lltL, and RRL this may be done by substituting such system for the appara each channel located between the line and the series and shunt resistances for controlling the amount ol'i carrier current from said source supplied to the line to transmit sig nals, whereby the transmission of disturbing variations between the channels of the different lines due to impedance changes therein during signaling is prevented.

2. In carrier transmission, a source of carrier currents, a plurality of transmission lines each having a carrier channel superposed thereon, means for supplying'carrier current of the same frequency from said source to a carrier channel of each line, a shunt resistance element and a series resist ance element in each of said channels, a signal transmitting element in each channel located between the line and said shunt and series resistance elements, said signal transmitting element being ada ted to intermittently short-circuit said s unt resistance element to'vary the amount of carrier nals, whereby variations in the amount of carrier current continuously drawn from said source during signaling operations is maintained within predetermined limits.

3. In carrier transmission, a plurality of transmission lines each having a carrier channel superposed thereon, a source of carrier currents, means for supplying carrier current of the same frequency from said source to a channel of each of said lines, series and shunt resistance elements in each channel, and means in each channel adapted to be connected in shunt thereto between certain of said resistance elements for intermittently varying the amount of carrier current applied to the line to transmit signals. 1

4. In carrier transmission, a plurality of transmission lines each having carrier channels superposed thereon, a common source supplying carrier current of the same frequency to a channel of each of said lines, a shunt resistance element and a plurality of series resistance elements in each of said channels supplied from said source, a signal transmitting element in each channel adapted to intermittently shortcircuit the shunt resistance element to control the amount of carrier current from said source supplied to the line to transmit signals, one of said series resistances in each channel being located between the signal transmitting element and the line, said one of said series resistances being of such value as to prevent during the operation of the signaling element in the channel such impedance changes as would cause disturbing variations to be transmitted between adjacent channels of the same line.

5. In carrier transmission wherein a plurality of transmitting channels of difi-erent carrier signaling systems are supplied with carrier currents of the same frequency from the same source; a band filter in each channel; and a modulator for each channel comprising impedances in series and bridged relation thereto, and means to intermittently change the electrical relation of one of said elements to the channel to control the signals transmitted, said impedances and the input surge impedance of the filter being so related that during'the transmission of signals the voltage variations of the input carrier currents to the channels are Within predetermined limits. Y

6. In carrier transmission wherein a plurality of transmitting channels of different carrier signaling systems are supplied with carrier currents of the same frequency from the same source; a band filter for each chan nel; and a modulator for each channel comprising impedances in series and bridged relation thereto, and means to intermittently short circuit the bridged impedance to control the signals transmitted, said impedances and the input surge impedance of the filter being so related that during the transmission of signals the voltage variations of the input carrier currents to the channels are within predetermined limits.

7. In a signaling system, the combination of a rectifier having an input and an output circuit, an input transformer connecting to the input circuit an incoming circuit over which signaling currents are transmitted, a signal receiver in the output circuit, and am- 7 plitude discriminating means including an impedance connected to said input circuit to reduce the efi'ect of incoming interfering line currents superposed on the signal currents on the operation of the signal receiver with respect to the efi'ect of said signal currents V on the operation of said receiver.

8. In a signaling system, the combination of a rectifier having input and output circuits, means to couple the input circuit to 80 an incoming transmission channel, a signal receiver in the output circuit, a source of current in the input circuit, and, a high impedance element in the input circuit positioned between and in series with the currentsource and the coupling means in said input circuit whereby the signal receiver is unaifected by incoming interfering channel currents.

9. In a signaling system, the combination of a rectifier having input and output circuits, means to couple the input circuit to an incomin transmission channel, a signal receiver in t e output circuit, a source of current in the input circuit, and a high resistance element positioned between and in series with the current source and the coupling means in said input circuit whereby the signal receiver is unaffected by incoming interfering channel currents.

10. In a multiplex carrier transmission system, the combination of aplurality of transmitting channels supplied with carrier currents of different frequencies; a main channel coupled to the transmitting channels; a band filter for each transmitting channel; and a modulator for each transmitting channel comprising impedances in bridged and series relation to the channel and form ing an input impedance termination for the filter thereof, and a transmitting element to change the electrical relation of one of said impedances to the channel to control the signals transmitted, said impedance and input surge impedance of the associated band filter being so related that during the transmission of signals the modulation between adjacent channels for a given frequency spacing is limited to a predetermined amount.

11. In a multiplex carrier transmission system, the combination of a plurality of transmitting channels supplied with carrier currents of different frequencies; a main channel coupled to the transmitting chan- 130 tionvfor the filter thereof, and a transmitting nels; a band filter for each transmitting channel; and a modulator for each; transmitting channel comprising impedances-in bridged and series relation to the channel and forming an input impedance termina-.

element to sliort circuit the bridged impedance to control the signals transmitted, said I iinpedances' andthe -1I1I)t surge impedance of the associated. band filter being so related that during the transmission of signals the modulation between adjacent channels for a given l're uency spaciugisdiniited to a prcdetermine amount.

'12. A multiplex carrier telegraph system comprising a plurality of transmitting channels coupled to a transmission line, means to supply to the respective channels carrier currents of different frequencies, a band filter in each channel modulating means for each channel, including a switch to intermittently short circuit the channel to provide marking and spacing signals, an in'ipedancc element to prevent short circniting the source of carrier current when v.the channel is ..hort circnited ,a'nd bridged and series elements whose combined impedance approximates the input surge im-, pedance of the bundfilter of the channel, the impedance of the series element being determined by the frequency spacing of the channels.

v 13. In a carrier signalin system, a transinittiu'g member movable between two contacts to control the application and withdrawal of carrier current to and from a transmission line, and a receiving relay associaited with the lineand having a working contact actuated in response to said carrier current to close only in response to the line current condition produced by engagement of said membcrwith one of its two contacts and to open only in response to the line current condition produced by engagement of said member with its otherjcontact.

14-. A carrier signaling system having in combination a source and means to modulate the-carrier oscilla tions to'form marking and spacing signals, saidinodulat ng means including a switch movable between two contacts connected the movement of the switch from one contact to the other andback to form a marking spacing signals,

iiig and spacing signal a transmitting chann'e of carrier oscillations, .a transmitting channel supplied thereby,

. engages the spacing and ending with carrier signal 5 beginning predetermined amplitude oscillations of a with the intermediate portion of t 0 signal of greater amplitude, V

15'. A carrier-signaling system having in combination a source of carrieroscillations, a transmitting channel transmission line coupled to the transmitting channel, and means to modulate the carrier oscillations to form marking and said modulating means including a switch inovablebetwee'n two contacts so connected with two impedance elements that I during the movement of the; switchfrom onecontact to the other and back again it dorms a marking signal beginning and endin with carrier oscillations of a' predetermined amplitude with the intermediate portion of greater amplitude.

16. A carrier telegra h system comprising a transmitting channe a source of carrier cscillations connected thereto, and means to modulate the carrier-oscillations, said means including a switch to intermittently open and close a circuit of low impedance bridged across the channel to provide marks an an impedance element under control of the switch included.

in series with the channel when the low impedance circuit is closed and removed electrieally' from the channel when the low inipedance circuit is opened.

17. A carrier telegraph system comprising oscillationstherefor, means to modulate the carrier, oscillations supplied to the channel to form marking and s acing signals, said inodulatingmeans inclu ing aswitch having connected thereto, a r

til

, a source of carrier assoc latedspacing and marking contacts, an

impet ance element in bridged relation to the channel and an impedance element inseries relation to the channel, and means so associating the switch andcoiitactswith the impedance elemei i'tsthat when the switch it engages the marking contaet the bridged elementis in circuit an the series element is in effect removed from circuit, when the switch is traveling between the contacts both elements are in circuit, and when the sw-itch' 14 contact 'th6'-'S6I.18S :elemer t is in circuit and the bridged element is in effect removed from circuit. In witnesswhereof, I hereunto subscribe iny ngimethis-Qfith day of March,- A. D. 1923.

Mansion BILoNe, 

